Lithographic apparatus, drying device, metrology apparatus and device manufacturing method

ABSTRACT

An immersion lithographic apparatus is described in which a two-phase flow is separated into liquid-rich and gas-rich flows by causing the liquid-rich flow to preferentially flow along a surface.

This application is a continuation of U.S. patent application Ser. No.14/498,883 filed on Sep. 26, 2014, now allowed, which is a continuationof U.S. patent application Ser. No. 12/543,011, filed on Aug. 18, 2009,now U.S. Pat. No. 8,953,142, which claims priority and benefit under 35U.S.C. § 119(e) to U.S. Provisional Patent Application No. 61/136,216,filed on Aug. 19, 2008, the content of each of the foregoingapplications is incorporated herein in its entirety by reference.

FIELD

The present invention relates to a liquid removal device, in particularthat can be used in or in conjunction with a lithographic apparatus or ametrology apparatus, as well as a method for liquid removal and devicemanufacture.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers and so-called scanners. In a stepper eachtarget portion is irradiated by exposing an entire pattern onto thetarget portion at one time. In a scanner each target portion isirradiated by scanning the pattern through a radiation beam in a givendirection (the “scanning”-direction) while synchronously scanning thesubstrate parallel or anti-parallel to this direction.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The liquid is desirablydistilled water, although other liquids can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with a higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may be regarded asincreasing the effective numerical aperture (NA) of the system andincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable are ahydrocarbon, such as an aromatic, e.g. Decalin, or a fluorohydrocarbon,or an aqueous solution.

Submersing the substrate or substrate and substrate table in a bath ofliquid (see, for example, U.S. Pat. No. 4,509,852) means that there is alarge body of liquid that must be accelerated during a scanningexposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

In an immersion apparatus, immersion liquid is handled by a fluidhandling system or apparatus. In an embodiment the fluid handling systemmay supply immersion fluid and therefore be a fluid supply system. In anembodiment the fluid handling system may confine fluid and thereby be afluid confinement system. If the confined fluid is a liquid, the fluidconfinement system may have a liquid confinement structure. In anembodiment the fluid handling system may provide a barrier to fluid andthereby be a barrier member. In an embodiment the fluid handling systemmay create or use a flow of fluid (such as gas), for example to help inhandling liquid such as to confine liquid for example as a contactlessgas seal. In an embodiment, immersion liquid may be used as theimmersion fluid. In that case, the fluid handling system may be a liquidhandling system.

One of the arrangements proposed is for a liquid handling system, suchas a liquid supply system. The liquid supply system is to provide liquidon only a localized area of the substrate and in between the finalelement of the projection system and the substrate using a liquidconfinement structure (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT Patent ApplicationPublication No. WO 99/49504. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet onto the substrate, desirably along thedirection of movement of the substrate relative to the final element.Liquid is removed by at least one outlet after having passed under theprojection system. That is, as the substrate is scanned beneath theelement in a −X direction, liquid is supplied at the +X side of theelement and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet and is taken up onthe other side of the element by outlet which is connected to a lowpressure source. In the illustration of FIG. 2 the liquid is suppliedalong the direction of movement of the substrate relative to the finalelement, though this does not need to be the case. Various orientationsand numbers of in- and out-lets positioned around the final element arepossible. One example is illustrated in FIG. 3 in which four sets of aninlet with an outlet on either side are provided in a regular patternaround the final element. Note that the direction of flow of the liquidis shown by arrows in FIGS. 2 and 3.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletsand can be arranged in a plate with a hole in its center and throughwhich the projection beam is projected. Liquid is supplied by one grooveinlet on one side of the projection system PS and removed by a pluralityof discrete outlets on the other side of the projection system PS,causing a flow of a thin film of liquid between the projection system PSand the substrate W. The choice of which combination of inlet andoutlets to use can depend on the direction of movement of the substrateW (the other combination of inlet and outlets being inactive). Note thatthe direction of flow of fluid and of the substrate W is shown by arrowsin FIG. 4.

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, the idea of atwin or dual stage immersion lithography apparatus is disclosed. Such anapparatus is provided with two tables for supporting a substrate.Leveling measurements are carried out with a table at a first position,without immersion liquid, and exposure is carried out with a table at asecond position, where immersion liquid is present. Alternatively, theapparatus has only one table.

PCT patent application publication WO 2005/064405 discloses an all wetarrangement in which the immersion liquid is unconfined. In such asystem substantially the whole top surface of the substrate is coveredin liquid. This may be advantageous because then the substantially wholetop surface of the substrate is exposed to the substantially sameconditions. This has an advantage for temperature control and processingof the substrate. In WO 2005/064405, a liquid supply system providesliquid to the gap between the final element of the projection system andthe substrate. The liquid between the final element of the projectionsystem and the substrate during exposure is optical liquid. That liquidis allowed to leak over the remainder of the substrate. A barrier at theedge of a substrate table prevents the liquid from escaping so that itcan be removed from the top surface of the substrate table in acontrolled way. The meniscus of the liquid defining the extent of theimmersion liquid is remote from the projection system. Although such asystem improves temperature control and processing of the substrate,evaporation of the immersion liquid may still occur. One way of helpingto alleviate that problem is described in United States patentapplication publication no. US 2006-0119809 in which a cover member isprovided which covers the substrate W in all positions. The cover memberis arranged to have immersion liquid extending between it and the topsurface of the substrate and/or substrate table which holds thesubstrate.

SUMMARY

In an immersion lithography apparatus, a two-phase flow (that is a flowof mixed liquid and gas) often arise. A two-phase flow can range from aflow in which there are droplets of liquid in a majority gas flow, tobubbles of gas in a majority liquid flow. Two-phase flow covers allpossibilities in between except where the gas is dissolved in the liquidor the gas and the liquid are separate and flow side by side in anorderly manner. For example, in a localized immersion system using a gasflow and liquid extraction to stabilize the meniscus of the immersionliquid, a substantial amount of liquid is swept up and extracted withthe gas of the stabilizing gas flow. A two-phase flow may cause aproblem. Evaporation of the immersion liquid into the gas, ifnon-saturated, can cause localized cooling. Two-phase flow is oftenunsteady, with, for example, a large volume of liquid interspersed withthe gas. Such unsteady flow can cause vibration due to the irregularmovements of a large volume of liquid and due to variation in thepressure in the extraction channel. Also, designing a pump and pipeworkto cope with gas, liquid and variable mixtures of gas and liquid addscomplication and expense.

It is desirable, for example, to provide an improved apparatus by whichtwo-phase flow can be stabilized and/or at least substantially separatedinto liquid and gas flows, and desirably substantially minimized.

According to an aspect of the invention, there is provided alithographic apparatus comprising a substrate table constructed to holda substrate, and a fluid handling structure arranged to remove liquidand gas in a two-phase flow from a surface of the substrate table, or ofa substrate held by the substrate table, or both the substrate table andthe substrate. The fluid handling structure comprises a phase separatorhaving a surface and arranged to separate the two-phase flow into afirst flow and a second flow. The first flow has a higher ratio ofliquid to gas than the two-phase flow and flows along the surface. Thesecond flow has a higher ratio of gas to liquid than the two-phase flow.

According to an aspect of the invention, there is provided a fluidhandling structure configured to remove liquid and gas in a two-phaseflow from a surface. The fluid handling structure comprises a phaseseparator having a surface and arranged to separate the two-phase flowinto a first flow and a second flow. The first flow has a higher ratioof liquid to gas than the two-phase flow and flows along the surface.The second flow has a higher ratio of gas to liquid than the two-phaseflow. In an embodiment, a drying device comprises the fluid handlingstructure. In an embodiment, an immersion metrology device comprises thefluid handling structure.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting an image of a pattern onto asubstrate through a liquid confined to a space adjacent the substrate.The method further comprises removing liquid from the substrate in atwo-phase flow with gas, and separating the two-phase flow into a firstflow and a second flow. The first flow has a higher ratio of liquid togas than the two-phase flow and flows along a surface. The second flowhas a higher ratio of gas to liquid than the two-phase flow.

According to an aspect of the invention, there is provided a liquid-gasseparator comprising a conduit or chamber divided into two parts by aporous plate, the first part being substantially filled with liquid. Theseparator further comprises a current generator configured to supplyliquid to the first part and constructed and arranged to generate acurrent in the liquid so as to substantially prevent bubbles of gasremaining on a surface of the porous plate which defines in part thefirst part. In an embodiment, a lithographic apparatus or a metrologydevice having an immersion system comprises the separator.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a fluid handling structure for use in alithographic projection apparatus;

FIG. 4 depicts a further fluid handling structure for use in alithographic projection apparatus;

FIG. 5 depicts parts of a substrate stage in an embodiment of theinvention, including a structure to handle fluid in order to control alocalized area of immersion liquid on a substrate held on a substratetable and a liquid removal device to remove liquid from the substrate;

FIG. 6 depicts other arrangements in the substrate stage of alithographic apparatus including a liquid removal device according to anembodiment of the present invention;

FIG. 7 depicts, in cross-section, a barrier member forming part of thefluid handling structure of FIG. 5;

FIG. 8 depicts, in cross-section, an arrangement in a barrier memberforming part of a fluid handling structure according an embodiment ofthe invention;

FIG. 9 depicts, in cross-section, a two-phase extraction arrangement ina barrier member forming part of a fluid handling structure according toa further embodiment of the invention;

FIG. 10 depicts, in cross-section, a two-phase extraction arrangement ina barrier member forming part of a fluid handling structure according toa further embodiment of the invention;

FIG. 11 depicts, in cross-section, a two-phase extraction arrangement ina barrier member forming part of a fluid handling structure according toa further embodiment of the invention;

FIG. 12 depicts, in perspective and partly cut-away, a two-phaseextraction arrangement in a barrier member forming part of a fluidhandling structure according to a further embodiment of the invention;

FIG. 13 depicts, in perspective and partly cut-away, a two-phaseextraction arrangement in a barrier member forming part of a fluidhandling structure according to a further embodiment of the invention;

FIG. 14 depicts, in cross-section, a two-phase flow in an ordinarycylindrical tube;

FIG. 15 depicts, in cross-section, a two-phase flow in a cylindricaltube usable in an embodiment of the invention;

FIG. 16 depicts, in cross-section, a two-phase flow in anothercylindrical tube usable in an embodiment of the invention;

FIG. 17 depicts in perspective a further cylindrical tube usable in anembodiment of the invention;

FIG. 18 depicts in perspective a further cylindrical tube usable in anembodiment of the invention;

FIG. 19 depicts in perspective a further cylindrical tube usable in anembodiment of the invention;

FIG. 20 depicts in perspective a further cylindrical tube usable in anembodiment of the invention; and

FIGS. 21A to 21D depict a liquid-gas separator usable in an embodimentof the invention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

an illumination system (illuminator) IL configured to condition aradiation beam B (e.g. UV radiation or DUV radiation);

a support structure (e.g. a mask table) MT constructed to support apatterning device (e.g. a mask) MA and connected to a first positionerPM configured to accurately position the patterning device in accordancewith certain parameters;

a substrate table (e.g. a wafer table) WT constructed to hold asubstrate (e.g. a resist-coated wafer) W and connected to a secondpositioner PW configured to accurately position the substrate inaccordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the radiation beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. The supportstructure MT holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structureMT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT maybe a frame or a table, for example, which may be fixed or movable asrequired. The support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more patterning device tables). Insuch “multiple stage” machines the additional tables may be used inparallel, or preparatory steps may be carried out on one or more tableswhile one or more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies. A fluid handlingstructure IH, which is described further below, controls a localizedarea of immersion liquid between the projection system PS and thesubstrate W.

The depicted apparatus could be used in at least one of the followingmodes:

-   1. In step mode, the support structure MT and the substrate table WT    are kept essentially stationary, while an-entire pattern imparted to    the radiation beam is projected onto a target portion C at one time    (i.e. a single static exposure). The substrate table WT is then    shifted in the X and/or Y direction so that a different target    portion C can be exposed. In step mode, the maximum size of the    exposure field limits the size of the target portion C imaged in a    single static exposure.-   2. In scan mode, the support structure MT and the substrate table WT    are scanned synchronously while a pattern imparted to the radiation    beam is projected onto a target portion C (i.e. a single dynamic    exposure). The velocity and direction of the substrate table WT    relative to the support structure MT may be determined by the (de-)    magnification and image reversal characteristics of the projection    system PS. In scan mode, the maximum size of the exposure field    limits the width (in the non-scanning direction) of the target    portion in a single dynamic exposure, whereas the length of the    scanning motion determines the height (in the scanning direction) of    the target portion.-   3. In another mode, the support structure MT is kept essentially    stationary holding a programmable patterning device, and the    substrate table WT is moved or scanned while a pattern imparted to    the radiation beam is projected onto a target portion C. In this    mode, generally a pulsed radiation source is employed and the    programmable patterning device is updated as required after each    movement of the substrate table WT or in between successive    radiation pulses during a scan. This mode of operation can be    readily applied to maskless lithography that utilizes programmable    patterning device, such as a programmable mirror array of a type as    referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may be employed additionally or in thealternative.

An embodiment of the present invention relates to an immersionlithographic apparatus. FIG. 5 depicts schematically, in plan, a fluidhandling arrangement relative to a substrate stage in more detail. Inparticular, a fluid handling structure 12 is provided to supply andcontrol immersion liquid flow in the lithographic apparatus. In anembodiment, the fluid handling structure is provided to supply andconfine an immersion liquid to a space between the final element of theprojections system PS (not shown in this figure) and the substrate Wand/or substrate table. (Note that reference to the substrate hereinincludes references to the substrate table in the alterative or as anaddition, unless stated to the contrary). This structure includes aliquid removal device 100 and is described further below. During thecourse of a series of exposures and measurements carried out on asubstrate W, the substrate table WT is moved relative to the projectionsystem PS and fluid handling structure 12 at high speeds and with highaccelerations. At various times, e.g. when exposing an edge die on thesubstrate and when making measurements using a sensor provided in sensorblock FID, the edge of the substrate may pass under the localized bodyof immersion liquid 11. This, and large accelerations or changes indirection of the substrate table WT, can cause a droplet or film tobreak away from the body of immersion liquid 11. A droplet can be leftbehind on the substrate, substrate table and/or sensor FID. A dropletleft on the substrate can cause problems, as discussed above. Thedroplet may cause localized cooling and hence distortion of thesubstrate. A droplet may deposit dissolved or suspended contaminantsand/or by attracting contaminants from the environment. Therefore, theliquid removal system 100 according to an embodiment of the invention isintended to minimize the creation of droplets left on the substrate bystabilizing the meniscus of the body of immersion liquid.

An additional liquid removal device 200 according to an embodiment ofthe invention may be provided to remove any liquid left on the substrateW. The liquid removal device 200 may be fixed in position relative tothe projection system so that the normal movement of the substrate tableunder the projection system during a series of exposures sweeps thesubstrate under it. The liquid removal device 200 may be provided withits own positioner. The liquid removal device 200 may be used when thefluid handling structure 12 does not have a liquid removal system 100according to an embodiment of the invention. For example the fluidhandling structure 12 may be of one of the types fluid handlingstructures depicted in FIGS. 2 to 4 and described above. Or it may be atype which uses a gas knife to confine the immersion liquid, e.g. asdisclosed in United States patent application publication no. US2004-0207824, incorporated herein by reference.

A liquid removal device according to an embodiment of the invention mayalternatively or in addition be placed at other positions in alithographic apparatus. For example, as shown in FIG. 6, a liquidremoval device 300 may be positioned between an exposure station, atwhich a substrate is exposed on substrate table WTa, and a measurementstation at which measurements are taken of, for example, a substrate onsubstrate table WTb. A measurement taken at the measurement station maybe a height map of the substrate using a level sensor LS. A substratesmay be loaded onto and off a substrate table at the measurement station.Liquid removal device 300 may be sufficiently large and suitablypositioned so that the whole of the substrate is swept as the substratetable passes beneath it when transferring between stations. A liquidremoval device 400 may be positioned at the measurement station to drythe substrate in conjunction with the taking of measurements. The liquidremoval device 400 may be provided with its own positioning system. Theliquid removal device may be located outside a lithographic device, forexample in the track. There it would have the same features as any ofthe liquid removal devices 200, 300, 400 herein described.

Another arrangement which has been proposed is to provide a fluidhandling system having a barrier member. Such an arrangement isillustrated in FIG. 7. In an embodiment, a seal is formed between thebarrier member and the surface of the substrate. In an embodiment, theseal is a contactless seal such as a gas seal. The seal may confine theimmersion liquid and so create a meniscus. Thus, near the seal is ameniscus of the immersion liquid. As exposure light passes through theconfined immersion liquid it may be considered optical liquid.

The fluid handling structure is schematically depicted in FIG. 7. Itforms part of a localized immersion system. The fluid handling structureis arranged to control, in particular to supply and to confine,immersion liquid to a space between the final element of the projectionsystem PS and the substrate W. The main part of the fluid handlingstructure is a barrier member 12, which extends along at least a part ofa boundary of the space between the final element of the projectionsystem and the substrate. The barrier member 12 is, in use,substantially stationary relative to the projection system in the XYplane though there may be some relative movement in the Z direction (inthe direction of the optical axis).

The barrier member 12 is a structure which may at least partly containliquid in the space 11 between a final element of the projection systemPS and the substrate W. Immersion liquid is provided via liquid supplyconduit 14, i.e. it is an inlet, and fills the space between thesubstrate surface and the final element of the projection system. Thespace is at least partly delimited by the barrier member 12 positionedbelow and surrounding the final element of the projection system PS.Liquid may be supplied to or removed from the space via inlet-outlet 13.The barrier member 12 may extend a little above the final element of theprojection system. The liquid level may rise above the final element sothat a buffer of liquid is provided. The barrier member 12 has an innerperiphery that at the upper end, in an embodiment, closely conforms tothe shape of the projection system or the final element thereof and may,e.g., be round. At the bottom, the inner periphery may closely conformto the shape of the image field IF, e.g., rectangular, though this neednot be the case.

The liquid 11 in the space is prevented from spilling out over the wholeof the surface of the substrate by liquid extraction conduit 15, formingpart of liquid removal device 100. Liquid extraction conduit 15 is influid communication with a plurality of orifices. The orifices formliquid openings which are disposed around the space occupied by theimmersion liquid. The shape and arrangement of these orifices serves tocontrol and in particular stabilize the meniscus 16 of the immersionliquid 11 so as to reduce or minimize droplets breaking away from orbubbles entering the immersion liquid. While a plurality of orifices oropenings are referred to herein, the plurality of orifices or openingsmay be a singular orifice or opening, which may be annular.

In an embodiment of the invention, the openings of the liquid removaldevice are conveniently defined by a plate that covers the lower surfaceof the barrier member 12 and has an appropriately shaped aperture orapertures. In an embodiment, the openings may be individual nozzles. Theopenings each may be co-planar with or protrude from the lower surfaceof the barrier member.

In localized immersion systems, liquid is only provided to a localizedarea of the substrate. The space 11 filled by liquid, i.e. thereservoir, is smaller in plan than the top surface of the substrate. Thereservoir remains substantially stationary relative to the projectionsystem PS while the substrate W moves underneath it. Another category ofimmersion system is the bath type arrangement in which the whole of thesubstrate W and optionally part of the substrate table WT is submersedin a bath of liquid. A further category is an all wet solution in whichthe liquid is unconfined. In this arrangement the whole top surface ofthe substrate and optionally all or part of the substrate table iscovered in a thin film of immersion liquid. Any of the liquid supplydevices of FIGS. 2 to 5 can be used in such a system; however, theirsealing features are not present, are not activated, are not asefficient as normal or are otherwise ineffective to seal liquid to onlythe localized area. Other arrangements are possible and, as will beclear from the description below, an embodiment of the present inventionmay be implemented in any type of liquid supply system.

In an immersion lithography apparatus, substantial quantities of theimmersion liquid are often extracted from the vicinity of the substrate.In doing so, it is common that gas, e.g. air from the environment, isextracted with the immersion liquid. This occurs in particular inlocalized fluid handling systems that use liquid extraction to pin themeniscus of the localized immersion liquid. When liquid and gas areextracted together in a two-phase flow, vibrations can be caused due toirregular flows that occur and/or because of fluctuations in thepressure at the extraction points due to that irregular flow. It istherefore desirable to separate the liquid and gas phases of a two-phaseflow at least partially, and desirably as much as possible. Completeseparation is often not necessary since a small proportion of gas in aliquid flow or a small proportion of liquid in a gas flow tends not tocause such undesired vibrations. Undesirable vibrations are avoided ifthe two-phase flow is homogeneous on the scale of the conduit, forexample a “bubbly flow” of small bubbles in liquid or a “misty flow” ofsmall droplets in gas. Partial separation is also desirable as it tendsto reduce the amount of evaporation of the liquid. This in turn reducesthe undesirable localized cooling caused by evaporation.

Therefore, an embodiment of the present invention provides alithographic apparatus comprising a substrate table and a fluid handlingstructure. The substrate table is constructed to hold a substrate. Thefluid handling structure is arranged to remove liquid and gas in atwo-phase flow from a surface of the substrate table and/or a substrateheld by the substrate table. The fluid handling structure comprises aphase separator having a surface and arranged to separate the two-phaseflow into a first flow and a second flow, the first flow having a higherratio of liquid to gas than the two-phase flow and flowing along thesurface, the second flow having a higher ratio of gas to liquid than thetwo-phase flow.

By causing a high liquid content flow (also referred to as a liquid-richflow) to flow along the surface, the two phases of the mixed two-phaseflow can be separated sufficiently to reduce undesirable vibrations anduneven flow. The liquid can be encouraged to flow desirably along thesurface by any one or combination of means as discussed below.

In an embodiment, the phase separator comprises a channel having firstand second walls and arranged so that liquid preferentially flows alongthe first wall, the first wall defining the surface. The shape of thechannel is designed to encourage the liquid to flow along the firstwall, e.g. by providing a change in direction such that centrifugalforce directs the liquid onto the first wall. Alternatively or inaddition, the shape of the channel may be such as to cause cyclonicflow, directing the liquid outwardly to the wall. Another possibility isthat the shape of the channel slows the two-phase flow sufficiently thatthe liquid separates out by or with the assistance of gravity.

In an embodiment, the first wall is more liquidphilic than the secondwall. By liquidphilic it is meant that the liquid has a contact angle tothe liquidphilic surface that is less than 90°, desirably less than 75°,50°, or 25°. The surface may be made liquidphilic by any suitablesurface treatment, for example a coating or by a surface relief, or maybe liquidphilic by virtue of the material from which it is made. Asurface relief may be a regular pattern or irregular roughness.

In an embodiment, the phase separator further comprises a wet chamberarranged so that liquid flowing along the first wall enters the wetchamber. In this way, the separation achieved at the surface can befixed, by directing the liquid-rich flow into a chamber from which itcan be removed separately from the gas-rich flow. It is desirable thatthe path of the liquid-rich flow is straight and/or tends downwardly.

In an embodiment, the wet chamber is connected to the channel by a slitdefined by the first wall and a divider. The width of the slit can bedefined by the divider so as to substantially ensure that the slit issubstantially filled by the liquid-rich flow at a flow rate expected inuse of the apparatus and thereby gas is kept out of the wet chamber.Also, the slit width can be chosen so that capillary forces encouragesubstantially only liquid to enter the slit.

In an embodiment, the phase separator comprises a dry chamber connectedto the channel via an opening in the second wall. The gas can then beextracted from the dry chamber, substantially without liquid.

In an embodiment, the first wall is curved so that at a point where thechannel enters the wet chamber the first wall is lower than the secondwall. With this arrangement, gravity assists flow of the liquid andseparation from the gas. Also, the first wall can be configured to forma dam that substantially prevents flow of the liquid back out of the wetchamber.

In an embodiment, the phase separator comprises a gas extraction channelseparated from the wet chamber by a gas-permeable liquidphobic membrane.The liquidphobic membrane substantially prevents liquid entering the gasextraction channel. A suitable material for the membrane depends on theimmersion liquid used. If the immersion liquid is water, a hydrophobicmembrane such as a porous fluoropolymer membrane, in particular athermo-mechanically expanded polytetrafluoroethylene (PTFE) and otherfluoropolymer product sold under the “Gore-Tex” trademark, may be used.

In such an embodiment, the phase separator may comprise a liquidextraction conduit projecting into the wet chamber and having an openingbelow the gas-permeable liquidphobic membrane. The position of theliquid extraction conduit can be set so that substantially only liquidis extracted and separation of the liquid and gas in the wet chamber isencouraged.

In an embodiment, the phase separator comprises a drain path. The drainpath allows liquid to drain from the wet chamber to a space between thesubstrate and a final element of a projection system arranged to projecta patterned radiation beam onto the substrate. With this arrangement theimmersion liquid can be directly recycled into the path of theprojection beam, reducing the flow of liquid into and out of the fluidhandling system.

In an embodiment, the phase separator comprises a chamber, defined byfirst and second walls, and a plurality of channels entering into thechamber through the second wall. The channels are arranged at an angleto the second wall such that a two-phase flow entering the chamber froma channel at least partially separates into a liquid flow along thefirst wall and a gas flow along the second wall. In such an embodiment,the direction of one or more channels and the shape of the chamber areeach designed to encourage separation of the liquid and gas. Forexample, one of the channels may be configured such that the two-phaseflow makes a sharp change of direction on encountering the first wall,thereby encouraging the liquid to flow along it.

In an embodiment, the phase separator further comprises a plurality offlow directing structures in the chamber adjacent the openings of thechannels. The flow directing structures can have curved surfaces thatdefine flow paths leading away from the openings, the flow paths flaringaway from the openings over at least part of their length. The curvedsurfaces can be arranged so that the flow paths turn through at least90°, desirable 180°. In this way the flow paths can ensure a suitableflow of the two-phase mixture to ensure that cyclonic and/or centrifugalforces cause the liquid to separate and desirably follow the first wall.

In an embodiment, the phase separator comprises a conduit having aliquidphilic surface, for example provided by a liquidphilic coatingprovided thereon and/or a liquidphilic surface relief provided thereon.As mentioned above, by liquidphilic it is meant that the liquid has acontact angle to the liquidphilic surface that is less than 90°,desirably less than 75°, 50°, or 25°.

In an embodiment, the phase separator comprises a conduit defined by awall and having a substantially circular cross-section over at least apart of the length thereof and a substantially helical structureprovided on the wall. The substantially helical structure can be asubstantially helical groove in the wall and/or a substantially helicalwire mounted on the wall. The groove and/or the wire can be providedwith a liquidphilic coating. Such a helical structure promotesestablishment and maintenance of a separated flow in which the liquiddesirably flows along the surface of the conduit and the gas flows downthe middle of the conduit. This may reduce turbulence and hencevibration.

In an embodiment, the conduit is in part defined by a wall in the formof a porous member, for example a porous plate such as a microsievethrough which liquid can be extracted. Microsieves are described furtherbelow and in US patent application publication no. 2006/0038968, whichdocument is hereby incorporated in its entirety by reference. In anembodiment, the phase separator further comprises a gas extractionconduit arranged within a part of the conduit so as to define an annulargap between an outer surface of the gas extraction conduit and an innersurface of the conduit. These arrangements enable the liquid and gasflows established around the outside and middle of the conduit to bedirected into separate channels, effectively fixing the separation.

In an embodiment, the fluid handling structure comprises a barriermember arranged to at least partly confine a liquid to a space betweenthe substrate and a final element of a projection system. The projectionsystem is arranged to project a patterned radiation beam onto thesubstrate. The phase separator is contained in the barrier member. Byproviding the separator in the barrier member, separation of the twophases can be effected as close as possible to the point(s) where thetwo-phase flow is taken up. In this way, the occurrence of vibration maybe minimized as much as possible.

An embodiment of the present invention also provides a fluid handlingstructure configured to remove liquid and gas in a two-phase flow from asurface. The fluid handling structure comprises a phase separator havinga surface and arranged to separate the two-phase flow into a first flowand a second flow. The first flow has a higher ratio of liquid to gasthan the two-phase flow and flows along the surface. The second flow hasa higher ratio of gas to liquid than the two-phase flow.

The fluid handling structure may be used in a drying device (which mayalso be referred to as a dryer) or an immersion metrology device forexample. The dryer may be part of a bath type or all wet immersionsystem, as described above, where immersion liquid is not confined to aportion of the substrate, but may flow over substantially all of thesurface of the substrate. In the dryer, the droplet remover removesliquid present on the surface of a substrate. In an embodiment thedrying may occur after exposure of the substrate is complete and beforethe substrate leaves the lithographic apparatus for processingelsewhere, for example, at a track for development, coating, baking andetching. In an embodiment the drying occurs after exposure in a separateunit outside the lithography apparatus. The drying may occur aftermeasurement in a metrology system where immersion liquid is used toreplicate an immersion environment.

To operate the dryer, the dryer may be passed over a substrate that hasbeen removed from the immersion system and/or the substrate may bepassed under the dryer. In an embodiment, the dryer is used with respectto the substrate once immersion liquid has been drained from theimmersion system and/or the liquid supply to the immersion system hasstopped. The liquid covering the substrate may break from a film to formmany droplets. As the dryer is used with respect to the substratesurface, liquid present on the substrate is removed, drying the surface.

An embodiment of the invention provides a device manufacturing method inwhich an image of a pattern is projected onto a substrate through animmersion liquid confined to a space adjacent the substrate, and liquidis removed from the substrate in a two-phase flow with gas. Thetwo-phase flow is separated into a first flow and a second flow, thefirst flow having a higher ratio of liquid to gas than the two-phaseflow and flowing along a surface, the second flow having a higher ratioof gas to liquid than the two-phase flow. The steps of projecting andremoving can be carried out simultaneously or the step of removing canbe carried out after the step of projecting has been carried out.

FIG. 8 is a cross-section of a part of a barrier member 12 a of a fluidhandling structure according to an embodiment of the present invention.The barrier member 12 a assists in confining an immersion liquid 11 to aspace between the final element of the projection system PS and thesubstrate W. Although only one side of the barrier member 12 a is shown,it can be arranged to surround completely the localized immersion liquid11, for example being in the form of an annulus. Also, although shown ashaving a vertical inner wall with a step, the inner wall may have othershapes, for example slanted as shown in FIG. 7, and in particular mayconform to the contour of the lower part of the projection system PS.

As shown in FIG. 8, there is a narrow gap between the lower surface ofbarrier member 12 a and substrate W through which the immersion liquidcan escape. In an embodiment this gap may be made as narrow and as longas possible to reduce or minimize the escape of immersion liquid. Anyliquid that does escape is extracted via opening 121. Opening 121 isconnected to an underpressure and draws in fluid, e.g. immersion liquid11 as well as gas, e.g. air, from the local environment. Opening 121 maybe a continuous slit extending completely around the localized area ofimmersion liquid 11 or a series of smaller slits together substantiallysurrounding the localized immersion liquid 11. For structural reasons,the opening 121 may be bridged at certain points by small connectors.

Opening 121 is defined by first wall 122 and second wall 123. First wall122 is on the side of the region of immersion liquid 11. Immersionliquid 11 will tend to flow up that wall 122. The preferential flow ofliquid 11 along first wall 122 can be encouraged by making first wall122 have a smaller contact angle, e.g. smaller than 90 degrees (e.g.,substantially smaller than 90 degrees), than second wall 123, e.g. byproviding a coating or surface relief on first wall 122 or by selectingthe material from which wall 122 is made. Similarly, second wall 123 canbe made of a selected material, coated or treated to have a highercontact angle to the liquid 11. The preferential flow of immersionliquid 11 along wall 122 begins the separation of the liquid and gasentering opening 121. This separation can be fixed, or conserved, bydirecting the high liquid content and high gas content portions of theflow into respective different chambers.

This can be achieved in the embodiment of FIG. 8 by divider 124 which ispositioned adjacent and substantially parallel to first wall 122 so asto define a channel, e.g. a capillary 125. Liquid 11 flowing up wall 122enters channel 125 and then wet chamber 126. The width of channel 125,as well as the surface coating thereon if desired, encourages liquid toenter but not gas. In an embodiment, the width of channel 125 is in therange of from 0.5 mm to 3 mm, desirably 1 mm to 2 mm. The gas, which ismore easily diverted, enters dry chamber 127 via a gap between divider124 and second wall 123. Divider 124 does not need to be vertical: itcan be oriented at other a different angle. Divider 124 can be formed bya microsieve (described further below) or a liquid-phobic porousmembrane (described further below) to effect further separation byallowing movement of gas or liquid substantially only in one directionbetween the chambers. The end of divider 124 is shown as tapering inFIG. 8 however this end can instead be flat or rounded. If tapered orrounded, the tapering or rounding can be provided on either or bothsides of the divider 124.

Wet chamber 126 and dry chamber 127 are connected to respective sourcesof under pressure, e.g. vacuum pumps (now shown). The sources extractthe liquid-rich and gas-rich flows from the wet and dry chambersrespectively and also provide the underpressure that draws the mixedtwo-phase flow into slit 121 in the first place. It is to be noted thatthe flow into wet chamber 126 and extracted therefrom may include somegas bubbles and similarly the flow of gas into dry chamber 127 andextracted therefrom may include some liquid droplets. It is notnecessary that the separation of liquid and gas be perfect at this stagebut sufficient separation to reduce the occurrence of uneven flow thatmay result in vibrations and/or reduce evaporation is desirable.

A barrier member 12 b according to an further embodiment of the presentinvention is shown in FIG. 9. As previously mentioned, barrier member 12b assists in confining an immersion liquid 11 to a space between a finalelement of projection system PS and substrate W. Some immersion liquidcan leak through the gap between barrier member 12 b and substrate W.Again the immersion liquid 11 and gas from the environment are drawn upinto slit 121. Slit 121 is defined by wall 122 a and 123 a which areeach configured to encourage separation of the two-phase flow enteringslit 121 into a liquid-rich flow along first wall 122 a and a gas-richflow along wall 123 a. In this embodiment, walls 122 a and 123 a aredesirably curved so that slit 121 turns from being vertical at itsentrance to being substantially horizontal or angled downwards at apoint where it meets separation chamber 128. At this point first wall122 a forms the lower side of slit 121. Thus, gravity assists in keepingthe liquid-rich flow along first wall 122 a. As the liquid-rich andgas-rich flows enter separation chamber 128, the liquid and gasnaturally tend to separate with the liquid occupying the lower part ofthe separation chamber 128. Desirably first wall 122 a has a lowercontact angle to the liquid 11 than second wall 123 a. This can beachieved in the same ways as detailed above.

A liquid extraction opening is provided by liquid extraction conduit 130which, in an embodiment, projects from the upper part of separationchamber 128 into the lower part and is connected to an under pressure(not shown) so as to extract liquid from the lower part of separationchamber 128. The level of the opening of the liquid extraction conduit130 can be set so as to control the level of liquid in the separationchamber 128. Depending upon the level of liquid in the chamber 128, somegas may also be extracted. This can be reduced or minimized by providinga microsieve. A microsieve is a porous member. In an embodiment themicrosieve may comprise a thin plate that has a large number of smallholes through it. By suitable control of the underpressure above themicrosieve, the size of the holes, and the liquid to be extracted, itcan be arranged that substantially only liquid passes through themicrosieve. The microsieve is desirably formed of a material having acontact angle to the immersion liquid of less than 90°, e.g.substantially less than 90°. By control of the underpressure above themicrosieve and by ensuring that there is always liquid above themicrosieve it is possible to prevent gas being extracted through themicrosieve. Further details of such microsieves are given in UnitedStates patent application publication no. US 2006/0038968 A1,incorporated by reference in its entirety. Suitable microsieves are madeby Stork Veco B.V. of the Netherlands.

To extract gas from the separation chamber 128, a gas extraction conduit131 is provided in the upper surface of the chamber 128. The entrance tothe gas extraction conduit 131 may be covered with a porous liquidphobicmembrane 132, such as a thermally expanded fluoropolymer membrane.Suitable membranes are commercially available, e.g. under the trademarkGORE-TEX®. If all the gas is extracted from the separation chamberthrough the membrane 132, the remainder of the fluid in the separationchamber is liquid and there may be no need for the above mentionedmicrosieve. If the separation chamber 128 is of suitable size and shape,the microsieve and porous liquidphobic membrane can be dispensed withand separation effected by positioning the liquid extraction opening inthe bottom of the chamber 128 and the gas extraction opening part in thetop of the chamber 128.

FIG. 10 shows a further barrier member 12 c that is a variation of thebarrier member 12 b shown in FIG. 9. In barrier member 12 c, opening121, formed by first and second walls 122 a, 123 a, is configuredsimilarly to opening 121 in barrier member 12 b of FIG. 9. Again, itfeeds the separating flows into separation chamber 128 where the liquidcontent separates out at the bottom. Rather than being extracted viaextraction conduit 130, an outlet 133 is provided near the bottom of theseparation chamber 128 opening into a channel 134 that leads back to thespace between the projection system PS and substrate W. This arrangementallows the immersion liquid to be recycled directly back to the spacebetween the projection system and the substrate. This can reduce theconsumption of the immersion liquid and also the volume of liquidflowing to and from the fluid handling structure. As in the structure ofFIG. 9, gas is extracted from separation chamber 128 through gasextraction conduit 131 whose entrance may be covered by optional porousliquidphobic membrane 132. Also shown in FIG. 10 is a controlled leak135 that provides a fluid communication between the local environmentand the upper part of the slit 121 and/or separation chamber 128. Thiscontrolled leak 135 includes a flow restrictor and may be used tocontrol the underpressure in slit 121 and separation chamber 128. Such acontrolled leak 135 may also be employed in other embodiments of theinvention.

In the embodiments described with reference to FIGS. 9 and 10, asubstantially horizontal microsieve (as described above) may be used todivide the separation chamber into two parts and to substantiallyprevent gas entering into the lower, liquid-filled part. In theembodiment described with reference to FIG. 10, gas and liquidextraction conduits similar to conduits 131 and 133 shown in FIG. 9 canbe provided to control the liquid level in chamber 128.

A further barrier member 12 f according to an embodiment of theinvention is shown in FIG. 11. In this embodiment, immersion liquid 11that passes along the gap between the barrier member 12 f and thesubstrate W is drawn into opening 121 along with gas from thesurroundings and so forms a two-phase flow in conduit 129. Additionalgas is supplied from gas source 136 to increase the amount of gas in thetwo-phase flow which then enters conduit 137. This, and the resultingincreased flow rate, encourages the two-phase flow to separate out inconduit 137. In conduit 137, the liquid flows in around the outside 138of the conduit while the gas flows mainly down the center 139. The innersurface of conduit 137 can be modified to encourage this as describedbelow with reference to FIGS. 14 to 17. In an embodiment, conduit 137 iswider than conduit 129.

Arrangements to divert the separated flows as described below withreference to FIGS. 19 and 20 can also be used. The additional gassupplied from gas supply 136 need not be the same as the gas taken upthrough opening 121. The additional gas can be taken from thesurroundings of the apparatus by a pump or can be a pressurized gassupply. Such an additional gas supply can be used in other embodimentsof the invention if desired.

A barrier member according to a further embodiment of the invention isshown in FIG. 12 in a partially-cut away perspective view. Shown in theFigure is the lower plate 140 of the barrier member 12 d. Lower plate140 is provided with a ring of small through-holes 141 through which theimmersion liquid is supplied to the space between the projection systemPS and the substrate W and a set of extraction ports 142 (only onedirectly visible in the Figure). A two-phase fluid flow comprisingliquid flowing underneath the bottom plate 140 and gas from the localenvironment is extracted through the extraction ports 142. Theextraction ports 142 lead to vertical channels 143 through the body ofthe barrier member 12 d. At their tops, the channels 143 open into agenerally horizontal separation chamber 144. Between adjacent conduits143, flow guiding structures 145 are provided. The flow guidingstructures have curved surfaces. With curved surfaces the flow guidingstructures 145 are generally semi-circular or semi-oval in plan. Theyare spaced apart so that passageways with diverging or widening wallsare defined between the top ends of the conduit 143 and the main part ofthe separation chamber 144. The passageways widen with an increase inthe distance from the top ends of the conduit 143. Omitted from FIG. 12is an upper surface in which may be defined openings for the exit ofliquid and gas from the separation chamber 144. The upper surface may bean upper plate of the barrier member 12 b. The upper plate may close theseparation chamber 144. The openings in the upper surface defineopenings of liquid and gas extraction channels. In an embodiment, asingle opening in the upper plate may be used. In this case the liquidand gas are arranged to flow separately in a single channel.

In use, the two-phase flow from the gap between the barrier member 12 dand the substrate W flows up channels 143. The flow then undergoes asharp change of direction to flow horizontally into the separationchamber 144. This sharp change of direction causes the liquid topreferentially flow along a surface of the separation chamber, such asthe underside of the upper plate which closes the upper side of theseparation chamber 144. The liquid flow thus separates from the mixedtwo-phase flow. The liquid flow leaves the remaining fluid, i.e. thegas, to flow as a gas flow.

Flow guiding structures 145 initially confine the flow exiting thechannels 143. The flow guiding structures 145 guide the two-phase flowaway from the channels 143. As the passageways between the flow guidingstructures widen with increasing distance from the channel 143, thesurface area of the passageways increases. With increasing passagewaysurface area, more of the liquid is drawn to flow along the surface ofthe separation chamber 144. The flow guiding structures 145 in effectallow the two-phase flow to spread out as it moves towards the center ofthe separation chamber 144. Thus with increasing distance from thechannel 143 the separation of the phases in the two-phase flow improves.

The flow guiding structures 145 may guide the gas and liquid flows (i.e.separated two-phase flow) to an opening. The two-phase flow leaves theseparation chamber as a separated two-phase flow, or as separated flowsof liquid and gas. Note that the opening through which the fluid exitsthe separation chamber 144 is desirably located in the upper surface.The opening may be defined in a surface of the chamber, for example in anon-limiting list: a lower surface of the chamber, a side surfacedefining a side of the chamber or a surface of the flow guidingstructure 145.

FIG. 13 is a partially cut-away perspective view of another barriermember 12 e according to an embodiment of the invention. Note that thefeatures shown in FIG. 13 are enlarged compared to those shown in FIG.12. The barrier member 12 e of FIG. 13 differs from barrier member 12 dof FIG. 12 in the shape and configuration of the flow guiding structures145, which are labeled as flow guiding structures 146.

In FIG. 13, flow guiding structures 146 have, in plan, a projection oneither side of an opening of the top of conduit 143. Each projection maybe a lobe with a curved surface. In plan, the flow guiding structure 146may be bilobed, with a recess between the lobes. The opening of theconduit may be located between the lobes and may be in the recess. Theadjoining, or inner, walls of each lobe of the bilobed structure maymeet to define a wall defining in part the opening to the conduit 143.The outer wall 146 b of the lobes of each bilobed structure define theremaining shape of the flow guiding structure. The outer wall of thelobes may converge to form a third lobe directed away from the bilobedstructure. The outer wall of the lobes near the third lobe may be aconverging or tapering part of the flow guiding structure. In anembodiment the flow guiding structure may be described as heart-shaped.The conduit 143 may open into the recess, which may be a cusp 146 a ofthe heart-shape.

A wall 147 of the separation chamber 144 opposing the lobes are shapedto correspond with the lobes. The shape of the wall defines a recess.Each recess is shaped (e.g., curved) away from the corresponding flowguiding structure 146. Adjoining recesses meet, in plan, at a point. Thepoint may be an edge. A point may be opposed to the opening of a conduit143, i.e. the wall of the flow guiding structure, between two lobes.

In use of the apparatus, the two-phase flow from conduit 143 is directedalong passageway 148. The passageway 148 is defined by a lobe of flowguiding structure 146 and a corresponding recess in the wall of theseparation chamber. The passageway may be curved. The two phase flow mayfollow a curved path along passageway 148. In the passageway 148, thetwo-phase flow may separate as it changes direction. The two-phase flowmay start to separate at this stage. The curved path of the two-phaseflow changes direction which in an embodiment may be by substantially180 degrees. The two phase fluid may then flow towards the main part ofthe separation chamber 144, and may be towards the tapering part.

The sharp change of direction on exit of the flow channel 143 combineswith a cyclonic effect generated by the movement of the flow throughpassageway 148 to cause the two-phase flow to start to separate (or inan embodiment separate) the two-phase fluid flow into separated flows ofliquid and gas. As the two-phase fluid flows along the passage betweenadjacent flow guiding structures 146, the phases of the two-phase flowmay continue to separate. Towards the tapering part 146 c, the walls ofa passage between the adjacent flow guiding structures 146 diverge. Thepassage widens. The surface area over which the two-phase flow flowsincreases to allow the fluid to spread out. As the phases of the fluidhave started to separate into liquid and gas, the increase in surfacearea may encourage the separation to increase. The two-phase flow may beextracted through openings of extraction channels defined in an uppersurface, for example in the upper plate (not shown) of the barriermember 12 e. The two-phase flow may be extracted through a singleopening as a flow in which the phases flow separately.

In an embodiment of the invention, it may be necessary to transport atwo-phase flow through a conduit which may be substantially circular incross-section. In order to help prevent uneven mixed two-phase flow,which may cause vibrations, it is desirable to separate the liquid andgas within the conduit which may be circular. In an embodiment of theinvention, the liquid content of the two-phase flow is encouraged toadopt an annular flow (i.e. annular two-phase flow) in an axialdirection of the conduit, radially outwardly from the gaseous flow. Thatis the liquid may flow along the outside inner surface of the conduitwhile the gas flows substantially along the middle of the conduit. Thiscan be achieved with an appropriate coating and/or structure in or onthe inner surface of the conduit.

FIG. 14 is a cross-sectional view of a circular cross-section conduithaving no particular surface treatment. There is a relatively highcontact angle between the liquid 11 and the wall of the conduit 150.Under the influence of gravity (if sufficiently stronger relative to theforces applied to the fluid to cause it to flow through the conduit) theliquid tends to flow along the bottom of the conduit 150. The liquid mayaccumulate into larger bodies filling the entire cross-section of theconduit. Such a cross-sectional blockage disrupts the smooth flow of thefluid, resulting in uneven flow, which may be referred to as plug-slugflow. In an embodiment of the invention, shown in FIG. 15, aliquidphilic coating 151 is on the interior wall of the conduit 150(i.e. a surface portion which may be treated which has a reduced contactangle relative to the surrounding surface). This reduces the contactangle between the liquid 11 and the wall of the conduit 150 (i.e. at thesurface portion). The liquid is caused to spread out over the interiorsurface of the conduit 150, for example the bottom of the conduit 150,into a liquid layer. The liquid layer reduces the tendency for theliquid 11 to form into a slug filling a cross-sectional portion of theconduit. Vibration caused by the flow may be reduced.

In an embodiment, shown in FIG. 16, liquidphilic surface relief pattern152 is formed on the interior wall of the conduit 150. As well asencouraging the liquid 11 to spread out more widely on the part of theconduit 11, this pattern 152 forms one or more pathways along which asmall stream of liquid can flow, again reducing the tendency of theliquid 11 to form a slug.

In an embodiment, a liquidphobic (increased contact angle) surfacerelief pattern may achieve a similar outcome. The patterning (whetherliquidphobic or liquidphilic) may be formed by a coating of material onthe conduit, a surface relief of the conduit, a physical structure suchas a projection or groove, or a combination of any of these features.The patterning may have a coiled pattern. The patterning may be appliedto an untreated surface, so that where the patterning is not applied, anadjustment or change to the contact angle of the surface does not occur.In an embodiment the effective surface is between patterned features. Inan embodiment the entire surface of the conduit may be a surface withadjusted contact angle; liquidphobic and liquidphilic patterning may bepresent in combination.

In an embodiment of the invention, a helical structure may be formed onthe inside of the conduit 150. This helical structure can take one or acombination of forms. For example, as shown in FIG. 17, a helical groove153 can be formed on the interior wall of the conduit 150, similarly torifling in a gun barrel. As shown in FIG. 18, a helical projection 154,e.g. wire, can be located substantially on the interior surface of theconduit. (In the case of wire, the wire can be inserted into theconduit). The projection 154 may be made of, or coated with, aliquidphilic material. Alternatively or additionally, not illustrated,the helical ridge (i.e. projection) is located on the interior wall ofthe coating. In each case, the helical structure encourages the liquid11 to flow in an annulus against the interior wall of the conduit 150.The depth or height of the groove, coil or ridge, its pitch and numberof starts can be selected based on the expected flow rates of liquid andgas in the two-phase flow. In an example, a 6 mm (internal diameter)hose was provided with an internal spring of stainless steel wire ofdiameter 0.5 mm having a pitch of 6 mm±2 mm. This arrangement may beeffective in providing smooth flow at a water ratio of about 1:250. Inan embodiment the pitch of the helical structure is greater than 50% ofthe diameter of the conduit. In an embodiment the pitch of the helicalstructure is substantially equal to or grater than the diameter of theconduit.

Having separated the two-phase flow within conduit 150 into annular flowor (where the two-phase flow is supplied as annular flow) maintainingthe annular flow, it is desirable to fix or conserve that separation bydiverting the liquid and gas into separate conduits. Two-phase annularflow may be supplied from a fluid handling structure shown in anddescribed with reference to FIGS. 12 and 13. So conduit 150 may beconnected to openings though which fluid exits separation chamber 144.

Two arrangements to help achieve fixation of the phase flow separationare shown in FIGS. 19 and 20. In FIG. 19, a part 155 of the wall of theconduit 150 is formed of a microsieve as described above. As mentionedabove, a microsieve may be a thin metal plate having a large number ofsmall holes formed therein, the size of the holes being determined sothat desirably only liquid passes through, especially if the space onthe other side of the sieve is filled with liquid. In this way, theliquid can be extracted from conduit 150 while the gas continues to flowdown conduit 150. In FIG. 20, a smaller tube 156 is inserted into thecenter of conduit 150 so that the gas flowing down the middle of conduit150 enters the smaller tube 156 and can therefore be separated from theliquid which preferentially flows around the interior wall of theconduit 150. This arrangement can of course be combined with themicrosieve arrangement of FIG. 19.

FIGS. 21A-D relate to a problem, and a solution therefor, that can occurwith the use of a microsieve to separate liquid and gas, as describedwith reference to FIGS. 8 and 9. FIG. 21A shows a conventional situationin which a microsieve 161 is used to separate or remove liquid 11 fromgas in a volume such as chamber 160. Chamber 160 is, for example,connected to a gap defined between the surface of a substrate table andthe surface of a substrate (commonly known as a substrate bubbleextraction system) or adjacent a restricted space, such as the undersideof a fluid handing structure 12. The microsieve 161 separates chamber160 from a volume e.g. an extraction conduit 164. The extraction conduit164 is filled with liquid. Through the extraction conduit 164, liquidextracted through the microsieve 161 may be removed. If an underpressureis applied to the extraction conduit 164 so as to withdraw the liquid 11through the microsieve 161 but no additional liquid enters the chamber160, a situation as shown in FIG. 21B, C can arise. What happens is thata bubble 162 may begin to develop on the surface of the microsieve 161within the extraction conduit 164 as the underpressure in the extractionconduit 164 increases. Once that bubble has formed, the surface tensioneffect that normally prevents gas passing through the microsieve 161ceases to operate locally and the bubble 162 may quickly expand to forma gas layer 163 adjacent the microsieve 161 within the extractionconduit 164, as shown in FIG. 21C. In this situation, additional liquidentering the chamber 160 can become trapped within the chamber 160. Gasinstead of liquid may enter the extraction conduit 164.

According to an embodiment of the invention, a solution is to provide acurrent within the liquid 11 in the conduit 164. The current may flow ina direction with a component which is perpendicular to the plane ofmicrosieve 161, for example in the surface of the microsieve in whichdefines in part the conduit 164. Desirably, the current may besubstantially perpendicular to the plane of the microsieve 161. Thiscurrent may be achieved by supplying additional liquid in one part ofthe extraction conduit 164 and extracting it in another part or simplyby setting up a recirculating flow of the liquid within the extractionconduit 164. The flow within the liquid 11 causes a bubble 162 to detachfrom the microsieve 161 before it can expand. The surface tension effectlimiting the passing of gas through the microsieve is maintained. Thisarrangement can result in small bubbles entering into the liquid in theextraction conduit 164 through the microsieve 161. However this isgenerally less undesirable than formation of a complete gas layer belowthe microsieve 161.

The embodiments described above provide various different arrangementsfor at least partially separating two-phase flow into separate flows:one with a relatively high liquid content (liquid-rich), one with arelatively low liquid content (gas-rich). Complete separation intoliquid and gas flows is not necessary; sufficient separation to reducevibration and/or evaporative cooling is desirable. Separation may occurin a single chamber or conduit. Subsequently such separation can besubstantially fixed by directing the separate flows into separatechambers or conduits.

Separation of a two-phase flow can occur in stages. The liquid-richand/or gas rich flows generated by any of the embodiments describedabove may be provided as input(s) to a separator or separator(s) of anyof the other embodiments, or to another similar stage. In this wayincreasingly complete separation can be achieved. In particular, anoutput of separation as described with reference to any of FIGS. 8 to 13may be conveyed and/or further separated by an arrangement as describedwith reference to any of FIGS. 15 to 21D.

An embodiment of the present invention may be applied to any two-phaseflow. In an immersion lithographic apparatus, particular sources oftwo-phase flows to which an embodiment of the invention may be used toseparate include: a dryer; a droplet or film removal device; and/or abubble extraction device (e.g., to extract liquid and gas from gapsbetween or below a substrate, a sensor or a closing disk and thesubstrate table or between a substrate table and a swap bridge or ameasurement stage, or a gap between a barrier member and a substrate orsubstrate table, or a gutter on a substrate table).

It may be desirable to effect separation of a two-phase flow as close toits source as possible. Thus, the phase separation according to anembodiment of the invention may be incorporated in a barrier member, asubstrate table, an extraction conduit, a swap bridge or a measurementstage.

In an embodiment of the invention, the effectiveness of the separationcan sometimes be improved by control of flow rates and pressures invarious parts of the apparatus. Such control may be effected by asuitable control system connected to sources of underpressure, sourcesof liquid and/or gas, and controllable valves, for example. The controlsystem may be embodied in software, hardware or a combination ofsoftware and hardware. A control system may be responsive to servos andor control systems of other parts of the apparatus so as to anticipateor respond to conditions and actions of other parts of the apparatusthat might affect the two-phase flow.

In an aspect, there is provided a lithographic apparatus comprising asubstrate table constructed to hold a substrate, and a fluid handlingstructure arranged to remove liquid and gas in a two-phase flow from asurface of the substrate table, or of a substrate held by the substratetable, or both the substrate table and the substrate, the fluid handlingstructure comprising a phase separator having a surface and arranged toseparate the two-phase flow into a first flow and a second flow, thefirst flow having a higher ratio of liquid to gas than the two-phaseflow and flowing along the surface, the second flow having a higherratio of gas to liquid than the two-phase flow. Optionally, the phaseseparator comprises a channel having first and second walls and arrangedso that liquid preferentially flows along the first wall, the first walldefining the surface. Optionally, the first wall has a lower contactangle than the second wall. Optionally, the phase separator furthercomprises a wet chamber arranged so that liquid flowing along the firstwall enters the wet chamber. Optionally, the wet chamber is connected tothe channel by a slit defined by the first wall and a divider.Optionally, the first wall is substantially straight between an inlet ofthe channel and the wet chamber. Optionally, the slit has a widtharranged so that capillary forces encourage substantially only liquid toenter the slit, desirably the slit width is in the range of from 0.5 mmto 3 mm, desirably from in the range of from 1 mm to 2 mm. Optionally,the first wall is curved so that at a point where the channel enters thewet chamber the first wall is lower than the second wall. Optionally,the phase separator further comprises a gas extraction channel separatedfrom the wet chamber by a gas-permeable liquidphobic membrane.Optionally, the phase separator further comprises a liquid extractionopening defined in a wall of the wet chamber, the liquid extractionopening being below the gas-permeable liquidphobic membrane. Optionally,the phase separator further comprises a drain path to allow liquid todrain from the wet chamber to a space between the substrate and aprojection system arranged to project a patterned radiation beam ontothe substrate. Optionally, the phase separator further comprises a drychamber connected to the channel via an opening in the second wall.Optionally, the phase separator comprises a chamber, defined by firstand second walls, and a plurality of channels entering into the chamberthrough the second wall, the channels being arranged at an angle to thesecond wall such that a two-phase flow entering the chamber from achannel at least partially separates into a liquid flow along the firstwall and a gas flow along the second wall. Optionally, the phaseseparator further comprises a plurality of flow directing structures inthe chamber adjacent the openings of the channels. Optionally, the flowdirecting structures have curved surfaces that define flow paths leadingaway from the openings, the flow paths increasing in width away from theopenings over at least part of their length. Optionally, the curvedsurfaces are arranged so that the flow paths turn through at least 90°,desirably 180°. Optionally, the phase separator comprises a liquidphilicsurface, desirably the liquidphilic surface is in a conduit. Optionally,the liquidphilic surface is a liquidphilic coating. Optionally, theliquidphilic surface has a liquidphilic surface relief provided thereon.Optionally, the phase separator comprises a conduit defined by a walland having a substantially circular cross-section over at least a partof the length thereof and a substantially helical structure provided onthe wall. Optionally, the substantially helical structure is asubstantially helical groove in the wall, or a substantially helicalwire mounted on the wall, or a contact angle surface patterning which ishelical, or any combination selected therefrom. Optionally, thesubstantially helical structure has a liquidphilic coating. Optionally,the phase separator further comprises a gas extraction conduit arrangedwithin a part of a conduit so as to define an annular gap between anouter surface of the gas extraction conduit and an inner surface of theconduit. Optionally, the surface is in part defined by a porous member,desirably a plate, through which liquid can be extracted. Optionally,the phase separator further comprises a gas supply arranged to addadditional gas to the two-phase flow. Optionally, the fluid handlingstructure comprises a barrier member arranged to at least partly confinea liquid to a space between the substrate and a projection systemarranged to project a patterned radiation beam onto the substrate, thephase separator being contained in the barrier member.

In an aspect, there is provided a fluid handling structure configured toremove liquid and gas in a two-phase flow from a surface, the fluidhandling structure comprising a phase separator having a surface andarranged to separate the two-phase flow into a first flow and a secondflow, the first flow having a higher ratio of liquid to gas than thetwo-phase flow and flowing along the surface, the second flow having ahigher ratio of gas to liquid than the two-phase flow.

In an aspect, there is provided a drying device comprising the abovefluid handling structure.

In an aspect, there is provided an immersion metrology device comprisingthe above fluid handling structure.

In an aspect, there is provided a device manufacturing method comprisingprojecting an image of a pattern onto a substrate through a liquidconfined to a space adjacent the substrate, removing liquid from thesubstrate in a two-phase flow with gas, and separating the two-phaseflow into a first flow and a second flow, the first flow having a higherratio of liquid to gas than the two-phase flow and flowing along asurface, the second flow having a higher ratio of gas to liquid than thetwo-phase flow. Optionally, the projecting and removing are carried outsimultaneously. Optionally, the removing is carried out after theprojecting has been carried out.

In an aspect, there is provided a liquid-gas separator comprising aconduit or chamber divided into two parts by a porous plate, the firstpart being substantially filled with liquid, and a current generatorconfigured to supply liquid to the first part and constructed andarranged to generate a current in the liquid so as to substantiallyprevent bubbles of gas remaining on a surface of the porous plate whichdefines in part the first part.

In an aspect, there is provided an apparatus having an immersion systemwith the above separator, wherein the apparatus is a lithographicapparatus or a metrology device.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the embodiments of the invention maytake the form of a computer program containing one or more sequences ofmachine-readable instructions describing a method as disclosed above, ora data storage medium (e.g. semiconductor memory, magnetic or opticaldisk) having such a computer program stored therein. Further, themachine readable instruction may be embodied in two or more computerprograms. The two or more computer programs may be stored on one or moredifferent memories and/or data storage media.

The controllers described above may have any suitable configuration forreceiving, processing, and sending signals. For example, each controllermay include one or more processors for executing the computer programsthat include machine-readable instructions for the methods describedabove. The controllers may include data storage medium for storing suchcomputer programs, and/or hardware to receive such medium.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath, only on a localized surface area of the substrate, or isunconfined. In an unconfined arrangement, the immersion liquid may flowover the surface of the substrate and/or substrate table so thatsubstantially the entire uncovered surface of the substrate table and/orsubstrate is wetted. In such an unconfined immersion system, the liquidsupply system may not confine the immersion liquid or it may provide aproportion of immersion liquid confinement, but not substantiallycomplete confinement of the immersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid outlets, oneor more gas outlets, one or more fluid outlets for two-phase flow, oneor more gas inlets, and/or one or more liquid inlets that provide liquidto the space. In an embodiment, a surface of the space may be a portionof the substrate and/or substrate table, or a surface of the space maycompletely cover a surface of the substrate and/or substrate table, orthe space may envelop the substrate and/or substrate table. The liquidsupply system may optionally further include one or more elements tocontrol the position, quantity, quality, shape, flow rate or any otherfeatures of the liquid.

It should be noted that the term “gas knife” should not be taken asrequiring that a specific gas is necessarily used, any gas or mixture ofgases may be used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

The invention claimed is:
 1. A lithographic apparatus comprising: aprojection system configured to project a radiation beam onto aradiation-sensitive substrate; a movable table; and a fluid handlingstructure configured to remove a fluid comprising a combination ofliquid and gas, the fluid handling structure comprising a barrier memberarranged to at least partly confine a liquid to a space between themovable table and the projection system, the barrier member comprising:an opening to remove the fluid, a porous member internal to the barriermember and facing toward the table, the porous member located downstreamof, and apart from, the opening and the porous member configured toreceive a part of the removed fluid separate from a remainder of theremoved fluid within the barrier member, and a conduit to discharge theremainder of the removed fluid.
 2. The lithographic apparatus of claim1, wherein the porous member is part of a duct to discharge the part ofthe removed fluid and the porous member is essentially liquidimpermeable.
 3. The lithographic apparatus of claim 1, wherein theporous member is part of a duct to discharge the part of the removedfluid and the porous member is essentially gas impermeable.
 4. Thelithographic apparatus of claim 1, further comprising a chamber withinthe barrier member, the interior of the chamber having an opening of theconduit and an opening of a duct to discharge the part of the removedfluid.
 5. The lithographic apparatus of claim 4, wherein the opening ofthe duct is lower than the opening of the conduit.
 6. The lithographicapparatus of claim 4, wherein at least part of the duct protrudes intothe chamber.
 7. The lithographic apparatus of claim 4, furthercomprising a liquid-phobic surface in the interior of the chamber. 8.The lithographic apparatus of claim 4, wherein the opening of the ductand the opening of the conduit are in, or attached to, an upper wall ofthe chamber.
 9. The lithographic apparatus of claim 4, furthercomprising a plurality of horizontal flow directing structures in thechamber.
 10. A lithographic apparatus comprising: a projection systemconfigured to project a radiation beam onto a radiation-sensitivesubstrate; a movable table; and a fluid handling structure arranged toremove a fluid comprising a combination of liquid and gas, the fluidhandling structure comprising a barrier member arranged to at leastpartly confine a liquid to a space between the movable table and theprojection system, the barrier member comprising: an opening to removethe fluid, a chamber, internal to the barrier member, arranged toreceive the removed fluid, the chamber having a generally horizontalwall in the interior of the chamber, a gas discharge opening in thechamber, the gas discharge opening configured to discharge primarilygas, and a separate liquid discharge opening in the chamber, the liquiddischarge opening configured to discharge primarily liquid.
 11. Thelithographic apparatus of claim 10, wherein the liquid discharge openingis located at a distal end of at least part of a discharge channelprotruding into the chamber.
 12. The lithographic apparatus of claim 10,wherein the liquid discharge opening comprises a porous member.
 13. Thelithographic apparatus of claim 10, wherein the gas discharge openingand the liquid discharge opening are in, or attached to, the generallyhorizontal wall of the chamber.
 14. The lithographic apparatus of claim10, wherein the liquid discharge opening is lower than the gas dischargeopening.
 15. The lithographic apparatus of claim 10, wherein theinterior of the chamber has a length in the horizontal larger than awidth in the vertical.
 16. The lithographic apparatus of claim 10,further comprising a liquid-phobic surface in the interior of thechamber.
 17. A lithographic apparatus comprising: a projection systemconfigured to project a radiation beam onto a radiation-sensitivesubstrate; a movable table; and a fluid handling structure arranged toremove a fluid comprising a combination of liquid and gas, the fluidhandling structure comprising a barrier member arranged to at leastpartly confine a liquid to a space between the movable table and theprojection system, the barrier member comprising: an opening to removethe fluid, a chamber, internal to the barrier member, arranged toreceive the removed fluid, a first discharge opening in the chamber, andat least part of a discharge channel protruding into the chamber andhaving a second discharge opening at a distal end thereof, the dischargechannel comprising a porous member.
 18. The lithographic apparatus ofclaim 17, wherein the first discharge opening is configured to dischargeprimarily gas and the second discharge opening is configured todischarge primarily liquid.
 19. The lithographic apparatus of claim 17,wherein the at least part of the discharge channel protrudes down froman upper wall of the chamber.
 20. The lithographic apparatus of claim19, wherein the first discharge opening is located at the upper wall.21. A lithographic apparatus comprising: a projection system configuredto project a radiation beam onto a radiation-sensitive substrate; amovable table; and a fluid handling structure arranged to remove a fluidcomprising a combination of liquid and gas, the fluid handling structurecomprising: a barrier member arranged to at least partly confine aliquid to a space between the movable table and the projection system,the barrier member comprising an opening through which the fluid isremoved, and a discharge conduit arranged to receive the removed fluid,the discharge conduit comprising a porous member on opposite sides of aflow path of the removed fluid through the discharge conduit, whereinprimarily liquid from the removed fluid passes through the porous memberand primarily gas continues to flow along the flow path.